not testing py37 with test_mnist_async because the test is intended to only test the latest version

Author: Chuyang Deng

tests/integ/test_tf_script_mode.py

@@ -164,7 +164,7 @@ def test_mnist_async(sagemaker_session, cpu_instance_type, tf_full_version, py_v
         role=ROLE,
         train_instance_count=1,
         train_instance_type="ml.c5.4xlarge",
-        py_version=py_version,
+        py_version=tests.integ.PYTHON_VERSION,
         sagemaker_session=sagemaker_session,
         script_mode=True,
         # testing py-sdk functionality, no need to run against all TF versions